1. Field of the Invention
The present invention relates to a printing quality enhancement via graphic/text detection method in compression (Joint Photographic Experts Group, JPEG) image, which is used on the equipment with output function, such as printers or multi-functional peripherals, and before printing, the energy parameters of the compressed image in the DCT (Discrete Cosine Transform) frequency domain are analyzed during the decompression process; moreover, with the help of a halftoning printing mode of automatic feedback-and-correction output equipment, the smoothness and sharpness of the output result can be improved.
2. Description of the Prior Arts
Graphic/text image normally consists of plural pixels, each of which includes three primary colors, red, green and blue. Each primary color is represented by a byte. In this case, a colorful picture of 512×512 pixels needs a memory space of 512×512×3 bytes=786K bytes. Obviously, the memory space is too large. To reduce the memory space of an image, conventional solution is to store the image in a compression format (JPEG). However, the detail features of the compressed image will be reduced according to the compression ratio, and as a result, the output image will be blurred.
Conventional solution for the image feature reduction is to divide the image into plural subimages by taking advantage of the similarity and continuity of the pixels, and then to determine by analyzing the features of the respective subimages the image block either text (feature attribute) or graphic (non-feature attribute). The related technologies are disclosed in U.S. Pat. No. 5,375,197 and U.S. Pat. No. 5,381,241.
In addition, TW Patent 426,834 discloses a printing quality enhancement method that is used to redistribute the edge pixels of the grayscale difference for images based on the theory of interpolation and Error Diffusion, for instance, to improve sharpness and smoothness of the edge of an image by imitating the edge distribution of 600DPI (Dots Per Inch) with an edge feature of 300DPI. The related technologies are also disclosed in U.S. Pat. No. 6,185,329 and U.S. Pat. No. 6,100,941.
According to the above-mentioned prior arts, when the image is transmitted to the output equipment (printer), it will help to improve image smoothness and sharpness, and the printing quality can be enhanced if the detail features of the image can be separately processed. Thus, the present invention provides a printing quality enhancement via graphic/text detection method in compression (JPEG) image.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages of the conventional technology.